diff --git a/examples/eval-tui/eval_tui/app.py b/examples/eval-tui/eval_tui/app.py
index bd15213..ab3369f 100644
--- a/examples/eval-tui/eval_tui/app.py
+++ b/examples/eval-tui/eval_tui/app.py
@@ -16,6 +16,7 @@
 from textual.app import App, ComposeResult
 from textual.widgets import Footer, Header, TabbedContent, TabPane
 
+from .help import HelpScreen
 from .models import RunSpec
 from .views import (
     BuildView,
@@ -92,6 +93,8 @@ class AgentixTUI(App):
         ("5", "show_tab('build')", "Build"),
         ("6", "show_tab('observability')", "Obs"),
         ("s", "save", "Save"),
+        ("t", "cycle_theme", "Theme"),
+        ("question_mark", "help", "Help"),
         ("q", "quit", "Quit"),
     ]
 
@@ -109,18 +112,39 @@ def action_save(self) -> None:
         path = view.export_to(Path.cwd() / "agentix-rollouts.json")
         self.notify(f"saved {len(payload['rollouts'])} rollouts → {path.name}", timeout=3)
 
+    def action_help(self) -> None:
+        """Toggle the key-binding cheatsheet."""
+        if isinstance(self.screen, HelpScreen):
+            self.pop_screen()
+        else:
+            self.push_screen(HelpScreen())
+
     def on_mount(self) -> None:
-        # Best-effort branded theme; falls back to the default if the running
-        # Textual version's theme API differs.
+        # Build the set of cycleable themes: a best-effort branded theme (falls
+        # back gracefully if the Textual version's theme API differs) plus a few
+        # always-available built-ins. Cycle with `t`.
+        self._themes: list[str] = []
         try:
             from textual.theme import Theme
 
             self.register_theme(
                 Theme(name="agentix", primary="#cc785c", secondary="#a45a45", accent="#e08a6d", dark=True)
             )
-            self.theme = "agentix"
+            self._themes.append("agentix")
         except Exception:
             pass
+        for name in ("tokyo-night", "gruvbox", "nord", "dracula", "textual-light"):
+            if name in self.available_themes:
+                self._themes.append(name)
+        if self._themes:
+            self.theme = self._themes[0]
+
+    def action_cycle_theme(self) -> None:
+        if not self._themes:
+            return
+        index = self._themes.index(self.theme) if self.theme in self._themes else -1
+        self.theme = self._themes[(index + 1) % len(self._themes)]
+        self.notify(f"theme: {self.theme}", timeout=2)
 
     def compose(self) -> ComposeResult:
         yield Header(show_clock=True)
diff --git a/examples/eval-tui/eval_tui/help.py b/examples/eval-tui/eval_tui/help.py
new file mode 100644
index 0000000..26dc881
--- /dev/null
+++ b/examples/eval-tui/eval_tui/help.py
@@ -0,0 +1,73 @@
+"""Help overlay — a modal cheatsheet of the app's key bindings.
+
+Pressing `?` pushes this screen; `?` / `escape` / `q` dismiss it. The rows are
+rendered from the running app's `BINDINGS` at display time, so the overlay
+cannot advertise a key the app doesn't actually bind (and can't drift as
+bindings change).
+"""
+
+from __future__ import annotations
+
+from textual.app import ComposeResult
+from textual.containers import Vertical
+from textual.screen import ModalScreen
+from textual.widgets import Static
+
+# Display labels for binding names that differ from what a user would type.
+_KEY_LABELS = {"question_mark": "?"}
+
+
+def _binding_rows(bindings: object) -> list[tuple[str, str]]:
+    """`(key, description)` for each described binding, read from a Textual
+    `BINDINGS` list (tuples or `Binding` objects). Bindings without a
+    description are omitted — they aren't user-facing."""
+    rows: list[tuple[str, str]] = []
+    for b in bindings or ():  # type: ignore[union-attr]
+        if isinstance(b, tuple):
+            key = b[0]
+            description = b[2] if len(b) > 2 else ""
+        else:
+            key = getattr(b, "key", "")
+            description = getattr(b, "description", "")
+        if key and description:
+            rows.append((_KEY_LABELS.get(key, key), description))
+    return rows
+
+
+def _render(rows: list[tuple[str, str]]) -> str:
+    width = max((len(key) for key, _ in rows), default=1)
+    return "\n".join(f"[b]{key.ljust(width)}[/]   {desc}" for key, desc in rows)
+
+
+class HelpScreen(ModalScreen[None]):
+    """Centered modal listing the app's key bindings."""
+
+    DEFAULT_CSS = """
+    HelpScreen {
+        align: center middle;
+        background: $background 60%;
+    }
+    #help-card {
+        width: auto;
+        height: auto;
+        max-width: 80%;
+        padding: 1 3;
+        border: round $primary;
+        background: $panel;
+    }
+    #help-title { padding-bottom: 1; text-style: bold; color: $accent; }
+    #help-foot { padding-top: 1; color: $text-muted; }
+    """
+
+    BINDINGS = [
+        ("escape", "dismiss", "Close"),
+        ("question_mark", "dismiss", "Close"),
+        ("q", "dismiss", "Close"),
+    ]
+
+    def compose(self) -> ComposeResult:
+        rows = _binding_rows(getattr(self.app, "BINDINGS", ()))
+        with Vertical(id="help-card"):
+            yield Static("Agentix TUI — keys", id="help-title")
+            yield Static(_render(rows), id="help-body")
+            yield Static("press ? or esc to close", id="help-foot")
diff --git a/examples/eval-tui/tests/test_app.py b/examples/eval-tui/tests/test_app.py
index 41f30e4..811b1dd 100644
--- a/examples/eval-tui/tests/test_app.py
+++ b/examples/eval-tui/tests/test_app.py
@@ -7,6 +7,7 @@
 
 from eval_tui.app import AgentixTUI
 from eval_tui.demo import DemoAgent, DemoDataset, DemoProvider
+from eval_tui.help import HelpScreen, _binding_rows
 from eval_tui.models import RunSpec
 from eval_tui.views.build import BuildView
 from eval_tui.views.catalog import CatalogView, discover_catalog
@@ -111,6 +112,46 @@ async def test_rollouts_export_to_writes_json(tmp_path: Path) -> None:
         assert len(loaded["rollouts"]) == 4
 
 
+async def test_theme_cycle_changes_theme() -> None:
+    app = AgentixTUI(rollout_spec=None)
+    async with app.run_test() as pilot:
+        await pilot.pause()
+        first = app.theme
+        await pilot.press("t")
+        await pilot.pause()
+        assert app.theme != first
+        assert app.theme in app._themes
+
+
+async def test_help_overlay_toggles() -> None:
+    app = AgentixTUI(rollout_spec=None)
+    async with app.run_test() as pilot:
+        await pilot.pause()
+        await pilot.press("question_mark")
+        await pilot.pause()
+        assert isinstance(app.screen, HelpScreen)
+        await pilot.press("escape")
+        await pilot.pause()
+        assert not isinstance(app.screen, HelpScreen)
+
+
+def test_help_rows_match_real_bindings() -> None:
+    # The overlay is derived from the app's BINDINGS, so every advertised key
+    # must map to a real binding (regression guard against a phantom row).
+    rows = _binding_rows(AgentixTUI.BINDINGS)
+    keys = {key for key, _ in rows}
+    descriptions = {desc for _, desc in rows}
+    bound_keys = {b[0] for b in AgentixTUI.BINDINGS}
+
+    assert {"Help", "Quit", "Overview"} <= descriptions
+    assert "?" in keys  # question_mark normalized for display
+    assert "t" in keys  # theme switcher is bound on this stack, so it's listed
+    # Every advertised key corresponds to a real binding (allowing the
+    # display-normalized '?' for 'question_mark').
+    for key in keys:
+        assert key in bound_keys or key == "?"
+
+
 async def test_build_view_constructs_command_from_path() -> None:
     app = AgentixTUI(rollout_spec=None)
     async with app.run_test() as pilot: